Thermoplastic elastomeric resin granule for powder molding

ABSTRACT

The present invention is a thermoplastic elastomeric resin granule for powder molding having a longer diameter of 400 μm or less and a ratio of the longer diameter to a shorter diameter of from 3:1 to 1:1, wherein said granule comprises a composition prepared by dynamically vulcanizing
         100 parts by weight of (a) a block copolymer consisting of at least two polymeric blocks (A) composed mainly of a vinyl aromatic compound and at least one polymeric block (B) composed mainly of a conjugated diene compound, and/or a hydrogenated block copolymer obtained by hydrogenating said block copolymer,   20 to 300 parts by weight of (b) a non-aromatic softening agent for rubber, and
 
10 to 150 parts by weight of (c) a peroxide-decomposing olefinic resin and/or a copolymer thereof. The resin granule has excellent fluidity in a powder molding.

FIELD OF THE INVENTION

The present invention relates to a thermoplastic elastomeric resingranule for powder molding.

PRIOR ART

Rotational powder molding method is widely used to produce a surfaceskin for automobile interior parts, such as instrumental panels, consoleboxes and the like. In the method, one can provide molded skin withleather grain patterns or stitches on their surfaces so as to attainsoftness to touch. In the rotational powder molding, powder should havegood fluidity in order to be cast uniformly on a mold surface with acomplicated shape, and removed easily if it did not adhere to the mold.

For the purpose of providing thermoplastic elastomeric resin powderhaving an improved fluidity, various kinds of thermoplastic elastomerand powder thereof were proposed. For example, Japanese PatentApplication Laid-Open H10-45976 discloses thermoplastic elastomer powderhaving a sphere-equivalent average diameter of larger than 0.7 mm to1.20 mm and a bulk density of at least 0.38, which thermoplasticelastomer is prepared by dynamically vulcanizing a compositioncomprising a polyolefin resin and ethylene-α-olefin copolymer rubber.Japanese Patent Application Laid-Open H10-81793 discloses powdercomprising the aforesaid resin composition and a hydrogenated conjugateddiene polymer or a random copolymer of a hydrogenated conjugated dienepolymer with a vinyl aromatic compound.

Japanese Patent Application Laid-Open H10-182900 discloses athermoplastic elastomer for powder slush molding comprising apolypropylene resin, hydrogenated styrene butadiene rubber, a processoil and an elastomer such as styrene/ethylene-propylene/styrene blockcopolymer and Japanese Patent Application Laid-Open H11-60826 disclosesa powdery resin composition comprising a polyolefin type polymer and ahydrogenated diene type polymer, wherein stickiness of the resins issuppressed so as to improve the fluidity.

These powder resins are prepared, for example, in a freeze-crushingmethod where the resin is frozen with liquid nitrogen or the like andcrushed in a mill such as a turbo mill, a roller mill, and a hammermill, or by extruding a resin through a die into a strand which is thendrawn, cooled, and subsequently cut, or by crushing the thermoplasticelastomer at a temperature of its glass transition or below, and thentreated with a solvent.

The powder, however, tends still to adhere and coagulate, and stillneeds improvement in its fluidity. Further, it is not easy to remove anexcess charge of the powder which has not adhered to a mold. Inaddition, the powder is difficult to handle on site and also causes aproblem due to dust.

Also, molded articles obtained from the aforesaid thermoplasticelastomers are not satisfactory in oil resistance and abrasionresistance. Where the thermoplastic elastomers are employed for a skinof a molded article, such as an automobile instrumental panel,comprising a core layer made of polyolefin and a middle foam layer madeof polyurethane, the skin should be recycled separately from the middlefoam layer.

Then, the purpose of the present invention is to solve the fluidityproblem in rotational powder molding of a thermoplastic elastomer.

Another purpose of the present invention is to provide a rotationalpowder molded article of a thermoplastic elastomer, which molded articleis excellent in oil resistance and abrasion resistance, and easy torecycle.

SUMMARY OF THE INVENTION

The present inventors have found that fluidity in rotational powdermolding can be drastically improved by making a thermoplastic elastomerinto granules of a predetermined shape and size instead of conventionalpowder. Thus, the present invention is a thermoplastic elastomeric resingranule for powder molding having a longer diameter of 400 μm or lessand a ratio of the longer diameter to a shorter diameter of from 3:1 to1:1, wherein said granule comprises a composition prepared bydynamically vulcanizing

-   -   100 parts by weight of (a) a block copolymer consisting of at        least two polymeric blocks (A) composed mainly of a vinyl        aromatic compound and at least one polymeric block (B) composed        mainly of a conjugated diene compound, and/or a hydrogenated        block copolymer obtained by hydrogenating said block copolymer,    -   20 to 300 parts by weight of (b) a non-aromatic softening agent        for rubber, and    -   10 to 150 parts by weight of (c) a polypropylene and/or a        copolymer composed mainly of propylene.

In a preferred embodiment of the invention, the aforesaid composition isprepared by kneading a composition prepared by dynamically vulcanizingthe components (a), (b) and (c), and 10 to 2,500 parts by weight of (d)at least one material selected from the group consisting of polyesterpolymers and copolymers, polyurethane polymers and copolymers, andpolyamide polymers and copolymers, per 100 parts by weight of thecomponent (a).

In another preferred embodiment of the invention, the followingcomponents (e) and (f) are also dynamically vulcanized:

-   -   0.01 to 15 parts by weight of (e) an unsaturated glycidyl        compound, and    -   0.01 to 15 parts by weight of (f) an unsaturated carboxylic acid        or a derivative thereof, per 100 parts by weight of the        component (a).        Preferably, 5 to 100 parts by weight of (g) a polyethylene        and/or a copolmer composed mainly of ethylene per 100 parts by        weight of the component (a) is also dynamically vulcanized, and        more preferably, 1 to 30 parts by weight of (h) a liquid        polybutadiene per 100 parts by weight of the component (a) is        also dynamically vulcanized.

The present granule may be prepared by an underwater cutting method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing size distributions of the present granuleand a freeze-crushed powder.

FIG. 2 is a microphotograph of the present granule at a 10×magnification.

FIG. 3 is a microphotograph of the present granule at a 60×magnification.

FIG. 4 is a microphotograph of a freeze-crushed powder at a 10×magnification.

FIG. 5 is a microphotograph of a freeze-crushed powder at a 60×magnification.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Each component of the present resin composition will be explained indetail.

Component (a), Block Copolymer

Component (a) used in the invention is a block copolymer consisting ofat least two polymeric blocks (A) composed mainly of a vinyl aromaticcompound and at least one polymeric block (B) composed mainly of aconjugated diene compound, or a hydrogenated block copolymer obtained byhydrogenating the aforesaid block copolymer, or a mixture thereof, suchas vinyl aromatic compound-conjugated diene compound block copolymershaving a structure, A-B-A, B-A-B-A or A-B-A-B-A, or those obtained byhydrogenating such. From such a block copolymer, a granule having adiameter almost as large as that of an extruder die can be obtained. Theblock copolymer and/or the hydrogenated block copolymer (hereinafterreferred to as (hydrogenated) block copolymer) contains 5 to 60% byweight, preferably 20 to 50% by weight, of a vinyl aromatic compound.Preferably, the polymeric block A composed mainly of a vinyl aromaticcompound consists solely of a vinyl aromatic compound or is acopolymeric block comprising more than 50% by weight, preferably atleast 70% by weight, of a vinyl aromatic compound and a conjugated dienecompound and/or a hydrogenated conjugated diene compound (hereinafterreferred to as (hydrogenated) conjugated diene compound).

Preferably, the polymeric block B composed mainly of a (hydrogenated)conjugated diene compound is composed solely of a (hydrogenated)conjugated diene compound or is a copolymeric block comprising more than50% by weight, preferably at least 70% by weight, of a (hydrogenated)conjugated diene compound with a vinyl aromatic compound.

The vinyl compound or the (hydrogenated) conjugated diene compound maybe distributed at random, in a tapered manner (i.e., a monomer contentincreases or decreases along a molecular chain), in a form of partialblock or mixture thereof in the polymeric block A composed mainly of avinyl aromatic compound or the polymeric block B composed mainly of a(hydrogenated) conjugated diene compound. When two or more of thepolymeric block A composed mainly of a vinyl aromatic compound or two ormore of the polymeric block B composed mainly of a (hydrogenated)conjugated diene compound are present, they may be same with ordifferent from each other in structure.

The vinyl aromatic compound to compose the (hydrogenated) blockcopolymer may be one or more selected from, for instance, styrene,α-methyl styrene, vinyl toluene and p-tert.-butyl styrene, preferablystyrene. The conjugated diene compound may be one or more selected from,for instance, butadiene, isoprene, 1,3-pentadiene, and2,3-dimethyl-1,3-butadiene, preferably butadiene and/or isoprene.

Any microstructure may be selected in the polymeric block B composedmainly of the conjugated diene compound. It is preferred that thebutadiene block has 20 to 50%, more preferably 25 to 45%, of 1,2-microstructure. In the polyisoprene block, it is preferred that 70 to 100% byweight of isoprene is in 1,4-micro structure and at lest 90% of thealiphatic double bonds derived from isoprene is hydrogenated.

A weight average molecular weight of the (hydrogenated) block copolymerwith the aforesaid structure to be used in the invention is preferably5,000 to 1,500,000, more preferably 10,000 to 550,000, further morepreferably 100,000 to 550,000, particularly 100,000 to 400,000. A ratioof the weight average molecular weight (Mw) to the number averagemolecular weight (Mn), Mw/Mn, is preferably 10 or less, more preferably5 or less, particularly 2 or less.

Molecule structure of the (hydrogenated) block copolymer may be linear,branched, radial or any combination thereof.

Many methods were proposed for the preparation of such block copolymers.As described, for instance, in JP Publication 40-23798/1965, blockpolymerization may be carried out using a lithium catalyst or a Zieglercatalyst in an inert solvent. The hydrogenated block copolymer may beobtained by hydrogenating the block copolymer thus obtained in thepresence of a hydrogenation catalyst in an inert solvent.

Examples of the (hydrogenated) block copolymer include SBS, SIS, SEBSand SEPS. A particularly preferred (hydrogenated) block copolymer in theinvention is a hydrogenated block copolymer with a weight averagemolecular weight of 50,000 to 550,000 which is composed of polymericblock A composed mainly of styrene and polymeric block B which iscomposed mainly of isoprene and in which 70 to 100% by weight ofisoprene has 1,4-microstructure and 90% of the aliphatic double bondsderived from isoprene is hydrogenated. More preferably, 90 to 100% byweight of isoprene has 1,4-microstructure in the aforesaid hydrogenatedblock copolymer.

Component (b), Non-Aromatic Softening Agent for Rubber

Non-aromatic mineral oils and non-aromatic softening agents liquid orlow molecular weight synthetic may be used as component (b) of theinvention. Mineral oil softening agents used for rubber are mixtures ofaromatic cyclic ones, naphthenic cyclic ones and paraffinic ones. Thosein which 50% or more of the whole carbon atoms is in paraffinic chainsare called a paraffinic type; those in which 30 to 40% of the wholecarbon atoms is in naphthenic rings are called a naphthenic type; andthose in which 30% or more of the whole carbon atoms is in aromaticrings are called an aromatic type.

Mineral oil softening agents for rubber to be used as component (b)according to the invention are of the aforesaid paraffinic or naphthenictype. Aromatic softening agents are improper, because they makecomponent (a) soluble and hinder the crosslinking reaction so thatphysical properties of a composition obtained are not improved.Paraffinic ones are preferred as component (b). Among the paraffinicones, those with a less content of aromatic cyclic components areparticularly preferred.

The non-aromatic softening agents for rubber have a kinetic viscosity at37.8° C. of 20 to 500 cSt, a pour point of −10 to −15° C. and a flashpoint (COC) of 170 to 300° C.

The amount of the component (b) to be blended is 20 to 300 parts byweight, preferably 40 to 300 parts by weight, more preferably, 80 to 200parts by weight, most preferably 100 to 170 parts by weight, per 100parts by weight of the component (a). If the amount is higher than 300parts by weight, the softening agent tends to bleed out to possibly makea final product sticky and be worse in mechanical properties. If theamount is less than 20 parts by weight, a resultant composition showsworse moldability. Component (b) preferably has a weight averagemolecular weight of 100 to 2,000.

Component (c), Polypropylene or a Copolymer Composed Mainly ofPropylene.

Component (c) attains an effect of improving dispersion of the rubber inthe composition obtained to thereby improve appearance of a moldedarticle. Component (c) is blended in an amount of 10 to 150 parts byweight, preferably 25 to 100 parts by weight, for 100 parts by weight ofcomponent (a). If the amount is less than 10 parts by weight,moldability of the elastomer composition obtained is deteriorated. If itexceeds 150 parts by weight, softness and rubber elasticity of theelastomer composition are deteriorated.

A Polypropylene and/or a copolymer composed mainly of propylene suitableas component (c) in the present invention has at least 20% ofrrrr/1-mmmm in a pentad ratio in a ¹³C— nuclear magnetic resonancemethod and a fusion peak temperature (Tm) of at least 150° C.,preferably 150 to 167° C., and fusion enthalpy (ΔHm) of at most 100 J/g,preferably 25 to 83 mJ/mg, as determined by differential scanningcalorimetry (DSC). Crystallinity may be estimated from Tm and ΔHm. If Tmand ΔHm are out of the aforesaid ranges, rubber elasticity at 100° C. orhigher of the elastomer composition obtained is not improved.

Polypropylene and/or a copolymer composed mainly of propylene suitableas component (c) in the present invention is high molecular weightpropylene homopolymers such as isotactic polypropylenes, or copolymersof propylene with a smaller amount of other α-olefine such as ethylene,1-butene, 1-hexene or 4-methyl-1-pentene. These resins preferably havean MFR (ASTM D-1238, Condition L, 230° C.) of 0.1 to 10 g/10 min., morepreferably 3 to 8 g/10 min.

If the MFR of the polypropylene and/or a copolymer composed mainly ofpropylene is less than 0.1 g/10 mm., moldability of the elastomercomposition obtained is deteriorated. If it exceeds 10 g/10 min., rubberelasticity of the elastomer composition obtained is deteriorated.

In addition to those described above, use may be made of a polypropyleneand/or a copolymer composed mainly of propylene composed of boilingheptane-soluble polypropylene having a number average molecular weight(Mn) of at least 25,000 and a ratio of Mw to Mn, Mw/Mn, of at most 7 andboiling heptane-insoluble polypropylene having a melt index of 0.1 to 104 g/10 min. or a polypropylene and/or a copolymer composed mainly ofpropylene composed of boiling heptane-soluble polypropylene having anintrinsic viscosity [η] of at least 1.2 dl/g and boilingheptane-insoluble polypropylene having an intrinsic viscosity [η] of 0.5to 9.0 dl/g.

Component (d), Polyester Type (Co)Polymer, Polyamide Type (Co)Polymer orPolyurethane Type (Co)Polymer

In the present invention, the polyester type (co)polymer, polyamide type(co)polymer or polyurethane type (co)polymer is not restricted toparticular one and any polymer and copolymer may be used satisfactorily.The copolymers may be a block or graft copolymer. The (co)polymers arepreferred to have elastomeric properties. Commercially availablepolymers may be used satisfactorily. The aforesaid copolymers areparticularly preferred. The aforesaid (co)polymers may be used alone orin a combination. Examples of the polyester type (co)polymer include(co)polymers in which a hard component is an aromatic polyester and asoft component is an aliphatic polyether, or in which a hard componentis an aromatic polyester and a soft component is an aliphatic polyester,or in which a hard component is polybutylene naphthalate and a softcomponent is an aliphatic polyether. Examples of the polyamide type(co)polymer include nylon-6, nylon-6,6, nylon-4,6, nylon-6,10,nylon-6,12, and block elastomers in which a hard component is polyamideand a soft component is polyetherr, or a hard component is polyamide anda soft component is polyetherester, wherein the polyamide is nylon-6 ornylon-12. Examples of the polyurethane type (co)polymer include lactonetype, ester type or ether type (co)polymers.

The amount of the component (d) to be blended is at least 1.0 part byweight, preferably at least 100 parts by weight, more preferably atleast 500 parts by weight and is at most 2,500 parts by weight,preferably at most 1,500 parts by weight, per 100 parts by weight of thecomponent (a). Particularly, it is preferred that polyester type(co)polymer is blended at least 150 parts by weight; polyamide type(co)polymer is blended at least 100 parts by weight; and polyurethanetype (co)polymer is blended at least 200 parts by weight. If the amountis more than 2,500 parts by weight, softness of the elastomercomposition obtained is decreased to be little different from that ofpolyester type (co)polymer, polyamide type (co)polymer or polyurethanetype (co)polymer.

In the present invention, blending of the component (d) drasticallyimproves oil resistance and stain resistance of a molded article. Inaddition, an automobile interior part consisting of a skin layer made ofthe present composition containing the urethane (co)polymer, an olefincore layer, and a middle foam layer made of urethane foam can berecycled by crushing the part altogether.

Component (e), Unsaturated Glycidyl Compound or Derivative Thereof

By subjecting the unsaturated glycidyl compound or derivative thereof tothe dynamic vulcanization, the resultant resin composition has improvedoil resistance and improved abrasion resistance. Preferably, a glycidylcompound having an unsaturated functional group which functional groupmay copolymerize with olefin, and a glycidyl group is used, such as,particularly, glycidyl methacrylate. Preferably, polyethylene andpolypropylene are modified by the unsaturated glycidyl compound orderivative thereof. That is, a soft component of the component (a),hydrogenated block copolymer, and component (c), peroxide-decomposingolefinic resin and/or a copolymeric rubber containing said resin, aremodified.

Component (e) is blended in an amount of at most 15 parts by weight,preferably at most 10 parts by weight, and at least 0.01 part by weight,preferably at least 0.1 part by weight, more preferably at least 3 partsby weight, for 100 parts by weight of component (a). If the amountexceeds the upper limit, heat deformation resistance and mechanicalproperties of the composition are deteriorated and, in addition, theeffect of improving compatibility of component (d), if blended, is notobserved.

Component (f), Unsaturated Carboxylic Acid or Derivative Thereof

By subjecting the unsaturated carboxylic acid or derivative thereof todynamic vulcanization, the resultant resin composition has improved oilresistance and abrasion resistance. Preferred examples of theunsaturated carboxylic acid or derivative thereof include acrylic acid,methacrylic acid, maleic acid, dicarboxylic acid or derivatives thereofsuch as acids, halides, amides, imides, anhydrides or esters.Particularly, maleic anhydride (MAH) is preferably used. Preferably,polypropylene and the like are modified by the unsaturated carboxylicacid or derivative thereof. That is, it is believed that a softcomponent in component (a), hydrogenated block copolymer, and component(c), polypropylene and/or a copolymer composed mainly of propylene aremodified.

Component (f) is blended in an amount of at most 15 parts by weight,preferably at most 10 parts by weight, and at least 0.01 part by weight,preferably at least 0.1 part by weight, more preferably at least 5 partsby weight, per 100 parts by weight of component (a). If the amountexceeds the upper limit, conspicuous yellowing occurs in the compositionand heat deformation resistance and mechanical properties of thecomposition deteriorate and, in addition, the effect of improvingcompatibility of component (d) is not observed.

Component (g), Polyethylene and/or A Copolymer Composed Mainly OfEthylene

As the polyethylene and/or a copolymer composed mainly of ethylene, usemay be made of one or more resin selected from the group consisting ofpolyethylene such as high density polyethylene (polyethylene prepared ina low pressure method), low density polyethylene (polyethylene preparedin a high pressure method), linear low density polyethylene (copolymersof ethylene with a smaller amount of α-olefin such as butene-1, hexene-1or octene-1); and olefinic copolymers such as ethylene-propylenecopolymer, ethylene-vinyl acetate copolymer, ethylene-acrylatecopolymer. Particularly preferred are an ethylene-octene copolymerhaving a density of at most 0.90 g/cm³ and ethylene-hexene copolymerhaving a density of at least 0.90 g/cm³ which are prepared using ametallocene catalyst (single site catalyst). When T_(m) of thesecopolymer is not higher than 100° C., it is necessary to add by the timeof crosslinking at the latest to crosslink them. T_(m) disappears by thecrosslinking and, therefore, fusion of octene or hexene does not occur.

One example of the component (g) is an olefinic polymer which isprepared using a catalyst for olefin polymerization which is prepared inaccordance with the method described in Japanese Patent ApplicationLaid-Open Sho-61-296008, which catalyst is composed of a carrier and areaction product of metallocene having at least one metal selected fromthe 4b group, 5b group and 6b group in the periodic table withalumoxane, the reaction product being formed in the presence of thecarrier.

Another example of the component (g) is an olefinic polymer preparedusing a metal coordinated complex described in Japanese PatentApplication Laid-Open Hei-3-163008, which metal coordinated complexcontains a metal selected from the group 3 (except scandium), groups 4to 10 and the lanthanoid group and a delocalized π-bonding partsubstituted by a constrained inducing part, and is characterized in thatsaid complex has a constrained geometrical form around said metal atom,and a metal angle between a center of the delocalized substitutedπ-bonding part and a center of at least one remaining substituted partis less than that in a comparative complex which is different from itonly in that a constrained inducing substituted part is substituted witha hydrogen, and wherein in each complex having further at least onedelocalized substituted π-bonding part, only one, per metal atom, of thedelocalized substituted π-bonding parts is cyclic.

Modified resin may also be used at need. Examples of such include(co)polymers modified with, for example, maleic anhydride, glycidylmethacrylate, allylglycidylether, oxazolyl methacrylate,allyloxazolylether, carboxylmethacrylate, allylcarboxylether, andpolymethylmethacrylate graft copolymers. Among these, anethylene-glycidyl methacrylate copolymer and a copolymer of maleicanhydride modified ethylene with glycidyl methacrylate are preferred.

The component (g) preferably has MFR determined at 190° C. and a load of2.16 kg of 0.1 to 10.0 g/10 min., more preferably 0.3 to 5.0 g/10 min.Component (g) is blended in an amount of at most 100 parts by weight,preferably at most 50 parts by weight, and preferably at least 5 partsby weight, more preferably at least 10 parts by weight, per 100 parts byweight of the component (a). If the amount exceeds the upper limit,softness of the resultant elastomer composition is lost and bleedout ofthe softening agent (b) tends to occur.

Component (h), Liquid Polybutadiene

Liquid polybutadiene is a polymer in which microstructure of a mainchain is composed of vinyl 1,2-bonding, trans 1,4-bonding and cis1,4-bonding and which is a transparent liquid at room temperature. Thevinyl 1,2-bonding amounts to preferably 30% by weight or less. If thevinyl 1,2-bonding exceeds 30% by weight, the properties of thecomposition obtained tends to deteriorate.

A number average molecular weight of the liquid polybutadiene ispreferably at most 5,000, more preferably at most 4,000, and preferablyat least 1,000, more preferably at least 3,000. If the number averagemolecular weight is below the lower limit, the heat deformationresistance of the composition obtained tends to become worse. If itexceeds the upper limit, the compatibility in the composition obtainedtends to become worse.

The liquid polybutadiene is preferably a copolymerizable compound havingone or more groups selected from epoxy, hydroxyl, isocyanate andcarboxyl groups. Among these, one having a hydroxyl group and acopolymerizable unsaturated double bond is particularly preferred, suchas R-45HT, trade mark, ex Idemitsu Petrochemical Co.

Component (h) is blended in an amount of at most 30 parts by weight,preferably at most 10 parts by weight, and at least 1 part by weight,preferably at least 3 parts by weight, per 100 parts by weight ofcomponent (a). If the amount is below the lower limit, effects ofblending is not observed, while if it exceeds the upper limit, themechanical properties of the composition is deteriorated.

Organic Peroxide

In the present invention, the components except component (d) aresubjected to dynamic vulcanization to thereby enable one to obtaingranules having almost the same diameter as that of the die. Examples ofthe organic peroxides used in the invention include dicumyl peroxide,di-tert.-butyl peroxide, 2,5-dimethyl-2,5-di(tert.-butylperoxy) hexane,2,5-dimethyl-2,5-di(tert.-butylperoxy) hexine-3,1,3-bis(tert.-butylperoxyisopropyl) benzene,1,1-bis(tert.-butylperoxy)-3,3,5-trimethylcyclohexane,n-butyl-4,4-bis(tert.-butylperoxy)valerate, benzoylperoxide,p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide,tert.-butylperoxy benzoate, tert.-butylperoxyisopropyl carbonate,diacetyl peroxide, lauroyl peroxide, and tert.-butylcumyl peroxide.

Among those, most preferred are2,5-dimethyl-2,5-di(tert.-butylperoxy)hexane,2,5-dimethyl-2,5-di(tert.-butylperoxy) hexine-3 and1,3-bis(tert.-butylperoxyisopropyl)benzene in terms of smell, coloringand scorch stability.

The amount of the peroxide to be added is at least 0.1 parts by weight,preferably at least 0.2 parts by weight, more preferably 0.6 parts byweight, and at most 3.0 parts by weight, preferably at most 2.5 parts byweight per 100 parts by weight of component (a). If the amount is lessthan 0.1 parts by weight, the required crosslinkage may not be obtained,while if the amount exceeds 3.0 parts by weight, the crosslinkingproceeds too much, causing poor dispersion of the crosslinked materials.

Crosslinking Aid

In the dynamic vulcanization in the present invention, it is preferredto use a crosslinking aid. The amount of the crosslinking aid is atleast 0.1 part by weight, preferably at least 1.0 parts by weight, morepreferably at least 2.0 parts by weight, and at most 10.0 parts byweight, preferably at most 8.0 parts by weight, more preferably 6.0parts by weight per 100 parts by weight of the component (a). If theamount is less than 0.1 part by weight, the crosslinking may not occursufficiently, and, if it exceeds 10 parts by weight, the crosslinkingefficiency tends to decrease. It is preferred that the amount of thecrosslinking aid added is about 1.0 to 3.0 times as large as the amountof the peroxide added.

In addition to the aforesaid components, the composition according tothe present invention may contain, if necessary, pigments, inorganicfillers, anti-oxidants, inorganic or organic blowing agents,flame-retardant such as hydrated metal compounds, red phosphorus,ammonium polyphosphate, antimony, and silicone.

The present granule may be prepared by, for example, the followingprocesses. In a first step, the components except component (d), e.g.,polyurethane resin, are kneaded under heating with a crosslinking agentbeing added. Preferably, a crosslinking aide is also added. Anyconventional means for kneading rubbers or plastics may be usedsatisfactorily, such as single screw extruders, twin screws extruders,rolls, Banbury mixers, and various kneaders. In this process, acomposition is obtained where each component is uniformly dispersed.

In the next step, the component (d), if desired, is added to the productof the first step and kneaded. Generally, the kneading is performed in asingle screw extruder, twin screws extruder, rolls, Banbury mixer, orvarious types of kneader. In this step, each component is furtherdispersed and at the same time the crosslinking reaction completes. Itis advantageous to side feed the component (d) to thereby perform thisstep consecutively after the dynamic vulcanization.

A twin screws extruder with an L/D ratio of 47 or more or a Banburymixer is preferred as the kneading means, because all of the steps maybe carried out continuously. For instance, when a twin screws extruderis operated at a screw rotation speed of 80 to 350 rpm, preferably 80 to200 rpm, each component is dispersed well to give good properties.

The present granule has a somewhat elongated spherical shape as shown inthe microphotographs (FIGS. 2 and 3). Because the shape is substantiallyspherical, good fluidity is attained. The terms “longer diameter” of thegranule herein means the longest diameter seen in a microphotographs atabout 20-30× magnification. A range of the longer diameter may bedetermined according to a mold shape, resin components and so on. Thelonger diameter should be small enough for the granule to be cast inevery corner of a mold without voids. However, if it is too small,advantages over conventional powder in the fluidity or handlingproperties are considered to be lost. In rotational powder molding of anautomobile interior parts, the longer diameter is preferably 400 μm orsmaller, and more preferably 360 μm or smaller. Further, a ratio of thelonger diameter to the shorter diameter, i.e., the shortest diameter ofthe diameters perpendicular to the longer diameters in themicrophotographs of the granule, is 3:1 or less, preferably 2:1 or less,more preferably 1.5:1 or less.

The above-mentioned granule may be prepared by an underwater cuttingmethod. In the underwater cutting method, granules are obtained byextruding the thermoplastic elastomer composition into water through anextruder die and cutting the extruded resin with blades provided in theclose proximity of the die. In the present invention, a cutting system,for example, Underwater Pelletizing Systems, ex Gala Industries Inc., isconnected to an extruder, where the extruded resin composition isimmediately cooled and cut. To obtain granules of the size specified inthe present invention, an output aperture of the die is 3 mm or smaller,preferably 1.0 mm or smaller, more preferably 0.3 mm or smaller. Athroughput of the thermoplastic elastomeric composition per output portof the die is typically 10 to 250 g/hr, preferably 20 to 100 g/hr. Atemperature of the water is typically 5 to 80° C., preferably 5 to 40°C. to prevent blocking of the die with the resin. An anti-blocking agentmay be added to the water.

Besides the underwater cutting method, other methods may be used where amolten resin composition is atomized by a spray or an atomizer and thencooled into granules.

EXAMPLES

The present invention is further elucidated with reference to thefollowing Examples and Comparative Examples. The values in the Tablesare expressed in parts by weight, unless otherwise indicated.

The following materials were used in the Examples and ComparativeExamples.

-   Component (a): hydrogenated block copolymer(SEPS-1), Septon 4077, ex    Kuraray Co.,    -   styrene content: 30% by weight,    -   isoprene content: 70% by weight,    -   number average molecular weight: 260,000,    -   weight average molecular weight: 320,000,    -   polydispersity: 1.23, and    -   hydrogenation ratio: at least 90%.-   Component (a): hydrogenated block copolymer(SEPS-2), Septon 2063, ex    Kuraray Co.,    -   styrene content: 13% by weight,    -   isoprene content: 87% by weight,    -   weight average molecular weight: 65,000,    -   hydrogenation ratio: at least 90%.-   Component (b): softening agent for rubber, Diana Process Oil, PW-90,    ex Idemitsu Kosan Co.,    -   tape: paraffinic oil,    -   weight average molecular weight: 540, and    -   aromatic component content: 0.1% or lower.-   Component (c): polypropylene and/or a copolymer composed mainly of    propylene PP, CJ700, trade mark, ex Mitsui Petrochemical Industries    Inc.,    -   Type: Polypropylene (PP)    -   MFR: 7 g/10 min.,    -   Crystallinity: Tm 166° C., ΔHm 82 J/mg.-   Component (d):    -   thermoplastic polyester type elastomer:        -   Hytrel 4068 (trade mark), ex Toray-DuPont Inc.,    -   thermoplastic polyamide type elastomer:        -   Pebax 5533SNOO (trade mark), ex Toray Inc.,    -   thermoplastic polyurethane type elastomer:        -   Elastran 1180A50 (trade mark), ex Takeda-Badisch Urethane-   Component (e): glycidyl methacrylate, ex Kanto Kagaku Co.-   Component (f): maleic anhydride, ex Kanto Kagaku Co.-   Component (g): polyethylene and/or a copolymer composed mainly of    ethylene Engage EG8150, ex Dow Chemical Japan Ltd,    -   type: metallocene catalyst type polyethylene (ethylene-octene        copolymer)    -   density: 0.868 g/cm ³.-   Component (h): liquid polybutadiene, R-45HT (trademark), ex Idemitsu    Petrochemical Industries Inc., having hydroxyl groups (acrylic type,    primary) and copolymerization-reactive unsaturated double bonds (1,4    bonds: 80%). The number average molecular weight is 2,800.-   Organic Peroxide: Peroxa 25B    (2,5-dimethyl-2,5-di(t-butylperoxide)hexane, ex Nihon Ushi Co.-   Crosslinking Aid: NK Ester IND (mixture of 85% of    2-methyl-1,8-octanedioldimethacrylate and 15% of    1,9-nonanedioldimethacrylate).-   Hydrogenated Styrene-butadiene Random Copolymer: Dynalon 1320P    (trade mark),    -   styrene content: 10 wt %, and    -   MFR (230° C., 2.16 kgf): 3.5 g/10 min.-   Polyvinyl Chloride Resin Compound:    -   polyvinyl chloride resin (straight resin), P-700, ex Shinnetsu        Chemical Co., degree of polymerization of 700, 100 parts by        weight,    -   pasty polyvinyl chloride resin (paste resin), PSL-10, ex        Kanegahuchi Chemical Co., degree of polymerization 1000, 17.6        parts by weight,    -   trimellitic acid ester type plasticizer, W-705, ex Dainippon Ink        & Chemical Inc., 76.5 parts by weight,    -   epoxidized soy bean oil, O-130, ex. Asahidenka Industries Co.,        5.9 parts by weight,    -   Ba-Zn type stabilizer 5.9 parts by weight, and    -   stearic acid 0.2 parts-by weight.-   Completely Crosslinked Olefinic Elastomer: Santplane 111-73, ex    A.E.S. Japan Ltd.-   Polyurethane resin: Pandex T-7890N (polycarbonate type), ex    Dainippon Ink &Chemical Inc.    Preparation Method

The components except component (d) were kneaded in the weight ratiosshown in Table 1 with a twin-screw extruder. Then, the peroxide and thecrosslinking aid were added and subjected to dynamic vulcanization at akneading temperature of 200° C., a screw rotation of 350 rpm and anextruder throughput of 20 kg/hr. After that, component (d) was side-fedand kneaded in Examples 2-9. At the exit of the extruder, a unit ofUnderwater Pelletizing Systems, ex Gala Industries, Inc., was installedto prepare granules having a longer diameter of about 0.3 mm.

In the Comparative Examples, the vulcanized compound was freeze-crushedand screened with a 42-mesh screen. A fraction of the powder whichpassed a 42-mesh screen was collected as a sample.

The samples obtained were tested for fluidity and moldability. Themolded articles from the samples were tested for abrasion resistance andoil resistance. The test methods are as described below. The resultsobtained are as shown in Table 1.

Test Method and Evaluation Criteria

1. Powder Fluidity Test

Fifty grams of each sample were put in a bulk density meter specified inJapanese Industrial Standards (JIS)K6721. After a damper of the densitymeter was opened, a time needed for an entire volume of a sample to flowout was measured.

Evaluation Criteria

-   -   ⊚: shorter than 15 seconds    -   ◯: shorter than 30 seconds    -   Δ: shorter than 60 seconds    -   x: 60 seconds or longer        2. Abrasion Resistance Test

An amount abraded was measured according to JIS K7204.

Evaluation Criteria

-   -   ⊚: less than 50 mm³    -   ◯: less than 100 mm³    -   Δ: less than 150 mm³    -   x: 150 mm³ or more        3. Oil Resistance Test

A molded article was immersed in IRM No.902 oil at 120° C. for 72 hoursand a volume change ratio relative to the original volume was measured.

Evaluation Criteria

-   -   ⊚: smaller than 30%    -   ◯: smaller than 50%    -   Δ: smaller than 100%    -   x: 100% or larger        4. Moldability Test

The granules obtained were put in a mold of 40 mm deep with a bottom of145 mm×145 mm and an opening of 165 mm×165 mm. The mold had aleather-like grain pattern on its inner surface. At that time, atemperature of the mold was 250° C. The opening of the mold was closedwith another mold and fixed together. The pair of the molds was rotatedin a reciprocating manner of 90 degrees around a rotational axis of asingle axis rotating instrument to let granules melt and adhere to thesurface of the mold. Then, the granules which did not adhere to thesurface of the mold were recovered. The molded article was taken outfrom the mold to which the granules had adhered, and then cooled. Acycle time for the molding procedure was measured and evaluated with thefollowing criteria.

Evaluation Criteria

-   -   ⊚: shorter than 90 seconds    -   ◯: shorter than 180 seconds    -   x: 180 seconds or longer

FIG. 1 shows a longer diameter distribution of the granules made by anunderwater cutting method in one Example in Table 1, and a sizedistribution of the freeze-crushed powder in one Comparative Example inTable 1. FIGS. 2-5 are photographs of the granules and the powder. InFIG. 1, the abscissa axis shows the mesh size. A ratio of the granuleswhich passed a 355 μm mesh screen and did not pass a 300 μm mesh screenwas ninety nine wt % of the granules according to the invention. On theother hand, the size of the freeze-crushed powder varied widely from 75to 355 μm. To narrow the size distribution, fractionation must befurther performed, which results in a worse yield of the powder tothereby increase production costs. The present granules are uniform witha much sharper size distribution compared with that of thefreeze-crushed powder. As seen in FIGS. 2 and 3, the present granule hasa substantially spherical shape. As a result, it is superior in fluiditycompared with the freeze-crushed powder having irregular shapes.Therefore, voids and pinholes in a molded article are avoided.

A size of the present granule is mainly determined by a size of anextruder die, but also depends somewhat upon a resin composition and adegree of crosslinking. In the present Examples 1-11, granules haddiameters almost as large as the die, except Example 6 where theurethane resin content was higher. The longer diameter of the granulewas determined as an average of the longer diameters of about 20granules, measured in a photograph. The granules made of the olefinicelastomer in Comparative Example 7 and those made of the polyurethaneresin alone in Comparative Example 9 had diameters about 1.5 times aslarge as the diameter of the die, so that they were not suitable forrotational powder molding due to their poorer flowability. InComparative Example 4, the granules of the composition which had notbeen dynamically vulcanized had diameters larger by about 10% than thediameter of the die. The granules of the hydrogenated SBR in ComparativeExample 3 had diameters larger by about 20% than the diameter of thedie. This may be due to the fact that the hydrogenated SBR is a randomcopolymer.

Generally, a polyurethane resin hardens slowly, so that a molded articletherefrom tends to deform if the article is taken out from a mold tooearly (see Comparative Examples 9 and 10). In the present invention, apolyurethane resin is blended with the dynamically vulcanizedthermoplastic elastomer, so that a time for hardening was reduced, ashape of a molded article was preserved better at a high temperature,the molding cycle time was reduced and the mold's surface embossment wasexcellently reproduced on the molded article (Examples 2 to 6,9 and 10).

The granules of the compositions containing the polyurethane resin orthe like in Examples 4 to 10 were superior in the oil resistance and theabrasion resistance, compared with the composition of the hydrogenatedSBR in Comparative Example 3 and the completely crosslinked olefinicelastomer in Comparative Examples 7 and 8. Particularly, the granulesfrom the composition of Example 6 showed almost the same level ofabrasion resistance as that of the granules of the polyvinyl chlorideresin. The oil resistance of the granules of the polyvinyl chlorideresin in Comparative Example 6 was very good at ambient temperature, butworsened at a higher temperature. The poor abrasion resistance of thegranules in Example 11 is considered to be due to the low miolecularweight of component (a).

INDUSTRIAL APPLICABILITY

As described above, the present granules

-   1) have a substantially spherical shape with a diameter of about 300    μm, so that they have excellent fluidity suited to rotational powder    molding;-   2) can be granulated consecutively after kneading, so that    production costs can be much lower than costs of a conventional    freeze-crushing process;-   3) have better handling properties than freeze-crushed powder; and-   4) provide molded articles which have excellent abrasion resistance,    oil resistance, and are easy to recycle, when they contain a    polyurethane resin.

TABLE 1 (Examples) Exam- Exam- Exam- Exam- Exam- Component ple 1 ple 2ple 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 ple 10ple 11 (a) SEPS-1 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0100.0 (a) SEPS-2 100.0 (b) Oil 75.0 125.0 125.0 125.0 125.0 125.0 125.0125.0 125.0 125.0 118.2 (c) PP 55.0 18.8 18.8 18.8 18.8 18.8 18.8 18.818.8 18.8 518.2 Organic peroxide 3.0 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.90.9 Crosslinking aid 5.4 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 (d)Polyurethane resin 615.7 615.7 395.8 615.7 1055.5 369.4 615.7 (d)Polyester resin 615.7 246.3 (d) Polyamide resin 615.7 (e) Glycidylmethacrylate 2.5 2.5 2.5 2.5 2.5 2.5 (f) Maleic anhydride 2.5 2.5 2.52.5 2.5 2.5 (g) PE 18.0 (h) Liquid polybutadiene 12.5 12.5 12.5 12.512.5 12.5 12.5 12.5 hydrogenated SBR 172.7 PVC compound Completelycross-linked Olefinic Elastomer Polyurethane resin Molding method U*¹ UU U U U U U U U U Average longer 300 300 300 300 300 350 300 300 300 300300 diameter (μm) Distribution of Narrow Narrow Narrow Narrow NarrowNarrow Narrow Narrow Narrow Narrow Narrow longer diameter Bulk density0.6 0.6 0.54 Fluidity ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ (seconds/50 g) 8 9 9 10 9 108 9 9 9 8 Moldability ⊚ ⊚ ⊚ ⊚ ⊚ ◯ ◯ ⊚ ⊚ ⊚ ⊚ Abrasion resistance ◯ ◯ ◯ ◯◯ ⊚ ◯ ◯ ◯ ◯ X (mm³) 98 98 98 90 70 45 97 90 75 90 150 Oil resistance ◯ ◯◯ ◯ ◯ ⊚ ⊚ ⊚ ⊚ ◯ ◯ (%) 49 45 45 44 34 27 20 10 28 40 40 (ComparativeExamples) Component CE*² 1 CE 2 CE 3 CE 4 CE 5 CE 6 CE 7 CE 8 CE 9 CE 10(a) SEPS-1 100.0 100.0 100.0 (a) SEPS-2 100.0 (b) Oil 125.0 125.0 118.2125.0 118.2 (c) PP 18.8 18.8 518.2 18.8 518.2 Organic peroxide 0.9 0.90.9 Crosslinking aid 1.7 1.7 1.7 (d) Polyurethane resin 395.8 1055.5395.8 (d) Polyester resin (d) Polyamide resin (e) Glycidyl methacrylate2.5 2.5 2.5 (f) Maleic anhydride 2.5 2.5 2.5 (g) PE (h) Liquidpolybutadiene 12.5 12.5 12.5 hydrogenated SBR 172.7 172.7 PVC compound100 Completely cross-linked 100 100 Olefinic Elastomer Polyurethaneresin 100 100 Molding method F*³ F U U F *** U F U F Average size (μm)150 150 350 320 200 150 450 170 500 180 Size distribution Wide WideNarrow Narrow Wide Narrow Narrow Wide Narrow Wide Bulk density 0.34 0.310.61 0.6 0.39 Fluidity ◯ ◯ ⊚ ⊚ ◯ ⊚ Δ Δ Δ Δ (seconds/50 g) 26 24 8 10 228 31 31 29 29 Moldability ⊚ ◯ ⊚ ◯ ◯ ⊚ ◯ ◯ X X Abrasion resistance ◯ ⊚ XΔ X ⊚ X X ⊚ ⊚ (mm³) 90 45 250 110 250 20 150 150 2 2 Oil resistance ◯ ⊚X Δ X X ◯ ◯ ⊚ ⊚ (%) 44 27 180 53 D*⁴ D 40 40 16 16 U*¹: Underwateroutting method CE*²: Comparative example F*³: Freeze-crushing methodD*⁴: Dissolved

1. A thermoplastic elastomeric resin granule for powder molding having a longer diameter of 300 to 355 μm and a ratio of the longer diameter to a shorter diameter of from 3:1 to 1:1, wherein said granule comprises a composition prepared by dynamically vulcanizing 100 parts by weight of (a) a block copolymer consisting of at least two polymeric blocks (A) composed mainly of a vinyl aromatic compound and at least one polymeric block (B) composed mainly of a conjugated diene compound, and/or a hydrogenated block copolymer obtained by hydrogenating said block copolymer, 20 to 300 parts by weight of (b) a non-aromatic softening agent for rubber, and 10 to 150 parts by weight of (c) polypropylene and/or a copolymer composed mainly of propylene.
 2. The thermoplastic elastomeric resin granule for powder molding according to claim 1, wherein said composition is prepared by kneading a composition prepared by dynamically vulcanizing the components (a), (b) and (c), and 10 to 2,500 parts by weight of (d) at least one material selected from the group consisting of polyester polymers and copolymers, polyurethane polymers and copolymers, and polyamide polymers and copolymers, per 100 parts by weight of the component (a).
 3. The thermoplastic elastomeric resin granule for powder molding according to claim 1 or 2, wherein the following components (e) and (f) are also dynamically vulcanized: 0.01 to 15 parts by weight of (e) an unsaturated glycidyl compound, and 0.01 to 15 parts by weight of (f) an unsaturated carboxylic acid or a derivative thereof selected from the group consisting of halides, amides, imides, anhydrides and esters, per 100 parts by weight of the component (a).
 4. The thermoplastic elastomeric resin granule for powder molding according to any one of claims 1 to 3, wherein 5 to 100 parts by weight of (g) polyethylene and/or a copolymer composed mainly of ethylene per 100 parts by weight of the component (a) is also dynamically vulcanized.
 5. The thermoplastic elastomeric resin granule for powder molding according to claim 1, wherein 1 to 30 parts by weight of (h) a liquid polybutadiene per 100 parts by weight of the component (a) is also dynamically vulcanized.
 6. The thermoplastic elastomeric resin granule for powder molding according to claim 1, wherein the granule is prepared by an underwater cutting method. 